Debt Senior Credit Agreement (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended		3 Months Ended	12 Months Ended			12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012 2011 Senior Credit Agreement [Member]	Dec. 31, 2011 2011 Senior Credit Agreement [Member]	Dec. 31, 2012 2012 Senior Credit Agreement [Member]	Sep. 30, 2011 2010 Revolving Credit Facility [Member]	Dec. 31, 2010 2010 Revolving Credit Facility [Member]	Dec. 31, 2011 Senior Term Loan [Member] 2011 Senior Credit Agreement [Member]	Dec. 31, 2012 Senior Term Loan [Member] 2012 Senior Credit Agreement [Member]	Dec. 31, 2012 Current Credit Facility [Member] 2012 Senior Credit Agreement [Member]
Deferred Finance Costs, Gross						$ 2,000,000
Debt Issuance Cost						6,300,000
Line of Credit Facility, Maximum Borrowing Capacity					300,000,000	300,000,000		400,000,000
Long-term Debt									450,000,000	425,000,000
Debt Instrument, Basis Spread on Variable Rate											0.75%
Debt Instrument, Description of Variable Rate Basis											.0175
Debt Instrument, Interest Rate at Period End										1.97%
Amortization of Financing Costs					1,100,000	300,000		1,100,000
Write Off Of Deferred Debt Issuance Cost	$ 12,466,000	$ 6,012,000	$ 6,636,000	$ 8,300,000			$ 2,500,000